Cx states not working on Dell Inspiron 8600 (Pentium M)

M. Warner Losh imp at bsdimp.com
Thu Aug 26 11:48:57 PDT 2004


In message: <412E2D33.1090900 at root.org>
            Nate Lawson <nate at root.org> writes:
: Ulrich Spoerlein wrote:
: > On Thu, 26.08.2004 at 09:37:33 -0700, Kevin Oberman wrote:
: > 
: >>The cx_usage is limited to C1 or C2 if USB is loaded. It's polling of
: >>the bus for changes prevents the state from dropping to anything really
: >>useful. If you don't always need USB, build a kernel without it and load
: >>it as required.
: > 
: > Ah, that explains it then. Is there anything that can be done about
: > that? Does that mean, that even Windows is not using C3 and C4 if there
: > is a USB mouse plugged in?
: 
: USB needs to be improved to poll more delicately.  I don't intend to 
: work on this any time soon but it's on the acpi todo list:
: 
: http://www.root.org/~nate/

This strikes me as something more properly belonging to the busdma
layer.  When there's bus mastering active, then we can't go into
C3/C4.  However, not all drivers in the tree are good about only
loading the DMA maps when a DMA is possible (but leaving it active all
the time, say), so maybe there's some wider-ranging problems that need
to be looked at as well.  While USB may also need some work to be
better about when it does DMA, I suspect that the problem is larger
than USB...  Why does the bus mastering that ATA does not a problem
while USB's is a problem?

Have you isolaged the USB agressive polling problem to some code I can
look at.  I have some usb code staring time on my plate for work and
it would be nice to know where to look.

Warner


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